Heres what you do, when you log into windows go into classic login mode by pressing ctl+alt+del, if your not already there. Then type in "administrator" as the user name. If you didn't set THE actual Admin password (as alot of people dont and set up there own account with admin rights) the password should be left blank. just hit enter and your in under the Admin account. Set up a password for that and any account your using with admin rights.

Secondly, if your in your computer and have admin rights. Select RUN type in CMD when the black CMD box appears type in "net user" (no quotes) this will give you a list of all accounts on your system, including the helpassist and support accounts. You might notice that there is an administrator account and other users. The great thing about this is you can change the passwords here without actually knowing them.
Re-type Net user followed by the account name listed and a *
example using soandso as the user name
C:\Documents and Settings\soandso>Net user soandso *
it then asks you to type in a password for the user. type carfully as you wont be able to see what you type,
Conferm that password and your done.

if you go in to safe mode is there an administrator account?
if so login in to it. it wont have a password on that account.
then go to control panel,users, select your user account and use the remove password option.
then restart and try to login as normal it shouldnt ask for password now.

using eiether xp home or pro the so called "secret administrator" account should appear in safe mode and have no password. this account can be used to take passwords of other accounts and any other admin task.

I did try just <enter> on the blank password space. It would not allow access. I also tried the 'Admin' account in safe mode, windows wanted a password here & likewise, would not take a blank field. OS = XP-Home.